1. Field of the Invention
The present invention relates to a sealant for covering a semiconductor element, and a semiconductor device, and more specifically relates to a silicone sealant for covering the surface of a semiconductor device component such as a substrate member or a lead frame, and to a highly reliable semiconductor device with superior moisture resistance and electrical insulation formed using such a semiconductor element sealant.
2. Description of the Prior Art
In order to protect a semiconductor element electrically, mechanically and chemically, prevent the migration of ion impurities and water from a molded resin such as an epoxy resin or a phenol resin into the element, and also prevent the cutting or passivation cracking of aluminum, gold or copper bonding wire arising from stress concentration produced by the molded resin, the surface of a semiconductor element is usually covered with a low elasticity resin with a low level of ionic impurities. Conventionally, these covering materials for semiconductor elements have utilized curable silicone sealants, which display good adhesion to the semiconductor element and excellent stress relaxation properties, and also offer low water absorption and excellent electrical insulation. Many semiconductor devices using such sealants have been proposed. Furthermore in recent years, methods have been proposed in which elements are sealed and shaped using screen printing techniques, either under conditions of normal pressure or under vacuum, although a sealant which has a sufficiently long pot life to enable satisfactory working, and yet undergoes rapid curing with good maintenance of shape and form is still keenly sought. In particular, addition reaction curing type silicone rubber sealants which utilize hydrosilylation can be cured within a short period of time by heating, and offer good levels of productivity with minimal generation of by-products during curing, and are consequently widely used. However, the curing reaction of addition reaction curing type silicone rubber compositions proceeds even at room temperature, meaning the compositions are prone to scorching and gelling, and the shortness of the pot life places considerable constraints on their workability.
As a result, improved techniques have been proposed for ensuring an adequate pot life. An example is the use of an acetylene compound with a boiling point of at least 25° C. (and preferably no more than 250° C.), as disclosed in Japanese Post-Examination Patent publication (kokoku) No. 44-31476 (JP44-31476B) corresponding to U.S. Pat. No. 3,445,420. However, when added to a silicone rubber composition, an acetylene compound of this application volatilizes readily and can cause partial scorching on the surface of the silicone rubber composition, and furthermore if cured under heating, can cause either corrugations on the surface of the cured product of the electrically insulating sealant, or internal foaming. In addition, because these acetylene compounds are volatile, as described above, they must be stored and handled in a sealed state, making them unsuitable for screen printing applications, which require a considerable length of time.
Furthermore, Japanese Laid-open Patent publication (kokai) No. 6-329917 (JP6-329917A) corresponding to U.S. Pat. No. 5,629,387 discloses the use of a hydroxyl group containing acetylene based compound represented by a formula R(R′)C(OH)—C≡CH (wherein, R and R′ represent monovalent hydrocarbon groups) in which the total number of carbon atoms contained within R and R′ is at least 9, and an organopolysiloxane based adhesion modifier formed from “Q” (SiO2) units and/or “T” (RSiO3/2) units, as a hydrosilylation reaction inhibitor and control agent. However, because the organopolysiloxane formed from the Q and/or T units is a varnish structure, the production of a homogeneous product with good stability is difficult, and the costs are also considerable. In addition, Japanese Laid-open Patent publication (kokai) No. 8-269339 (JP8-269339A) discloses the use of a hydroxyl group containing acetylene based compound represented by a formula R(CH3)C(OH)—C≡CH (wherein, R represents a monovalent hydrocarbon group of at least 9 carbon atoms) as a hydrosilylation reaction inhibitor and control agent, although no mention is made of the adhesive properties.